Augmented Reality (commonly referred to by the acronym AR) combines the “real world” reality view with a virtual view. The “real world” reality is the actual observable scene, one captured by a camera, or another optical or electronic sensor. The observable scene is determined by the camera location, direction of view and limitations of the actual environment (such as darkness, fog, smoke, and the like). In AR, computer generated images are combined with an actual or a representation of the observable scene. A computer renders additions to the environment based on an environment model that contains information required to render information of interest such as navigational aids and the like. Such rendition, generally referred to as overlay, may be a photo-realistic rendition of objects, a cartographical rendition, navigational data, and the like. In some cases, the most effective rendition comprises icons, textual data, pointers, and the like. Computerized environment models often comprise a combination of computer generated graphics with actual photographic data. Depending on the purpose of the system dynamic objects may be added through linking information provided by sensors like radar, sonar, magnetic, heat and other sensors that reflect a dynamically changing reality.
The viewpoint determines the viewable scene. The viewpoint is determined by the viewer coordinates, the direction of view, i.e. the x, y, and z coordinates and the heading (yaw), pitch and roll. The view itself is also determined by the horizontal and vertical field of view. A location sensor and an orientation sensor are provided to sense the direction of view, and allow the AR system to compute the viewpoint and to correlate the overlay with the observable scene in a process called registration. The overlay is merged with the observable scene image, in close registration thereto, to augment the visual information supplied to the user.
To increase clarity and brevity, these specifications will relate interchangeably to a combination of location and orientation as ‘LOR’, and to the combination of yaw, pitch, and roll as ‘YPR’.
The view is generated by a viewer, which may be an actual user's viewing a scene (most commonly via a viewing device in a see through system), but may also be an image sensor such as a camera, an optical sensor such as a periscope, fiber optic viewing device, and the like. In these specifications the viewer is generally used to denote a source from which the observable scene is inputted into the system. At a given point in time, the viewer has a viewpoint, which determine the observable scene.
An example of augmented reality system is presented in U.S. Pat. No. 6,208,933 to Lazar, directed to overlaying cartographic data on sensor based video. In this system cartographic data from a storage device is superimposed on data received from a video sensor. A location sensor is utilized to correlate the video image and the cartographic image.
AR systems are extremely beneficial for navigational purposes. A good example of navigational AR system may be found in U.S. Pat. No. 6,181,302 to Lynde, which discloses a marine navigation binoculars with virtual display superimposing real world image. The Lynde device uses orientation and positioning sensors, and overlays navigational and other data from several sources on the real world image. However a common disadvantage of these systems is the reliance on complex, heavy, and expensive location and orientation sensors.
Many LOR sensors exist that provide location and orientation parameters. The most common ones for location are based on GPS or inertial navigation technologies. For orientation, magnetic and gyroscopic, as well as light based systems are widely used.
It should be noted that most often the speed of location change tend to be far slower than the speed of YPR change. Moreover, for many practical applications the rate of location change is sufficiently small to permit the use of an inexpensive location sensor as the only means for location information. However changes in YPR are far faster, and thus require fast resolution. This is especially the case when the system is used to provide visual information such as in a marine or aerial navigation system, where the user perception is severely hampered by registration errors with the environment.
The existing YPR sensors suffer from compromises: Fast and accurate sensors (e.g. ring laser gyro based sensors) are prohibitively expensive for many applications. While inexpensive sensors generally provide orientation solution with sufficient accuracy, they require a long time to stabilize and thus are unsuitable for many applications that involve rapid motion in one or more axis. Marine and aviation navigation applications are especially vulnerable to the slow resolution time of those inexpensive sensors.
Examples of AR systems using different sensors may be seen in U.S. Pat. No. 4,802,757 to Pleitner et al., U.S. Pat. No. 6,453,223 to Kelly et al. and in US published application 2002/0069013 to Navab et al. U.S. Pat. No. 4,672, 562, U.S. Pat. No. 6,285,930 to Dickson et al. U.S. Pat. No. 4,866,626 and others.
Known solutions suffer the disadvantage of requiring training or placing objects in the environment, are slow, or are prohibitively expensive. If for example one of the uses of the system is entering into an environment for the first time, such as by a ship entering a new port, or an airplane flying over new terrain, or a combat team entering a hostile environment, the solutions provided are impractical. There is therefore a clear and unanswered need for a navigation system that will provide fast and efficient AR with good registration, and at reasonably low cost. The present invention aim at providing an apparatus and a method for answering this need.